EP0493202B1 - Light diffusing glass-sheet, method and apparatus for making it - Google Patents

Abstract

Light-scattering glazing sheet. It consists of a hot-laminated glass, the imprint impressed into the glass consisting of pyramidal craters separated from each other by distances which are smaller than their greatest dimension. In an alternative form, nonscattering areas are inserted beside the scattering regions. <??>The method and apparatus for producing the scattering glazing sheet also form part of the invention. <IMAGE>

Description

The invention relates to the field of glazing diffusing light and intended for lighting premises.

It has long been known to transform a transparent glass with parallel faces like a float glass, into glass diffusing light. The two most common techniques are sandblasting and chemical attack with a paste based on hydrofluoric acid. On the other hand, the techniques for laminating flat glass using rollers to reproduce on the surface of the glass the surface structure of the rollers, thereby producing printed glass are also well known. Both families of previous production methods allow both to obtain glazing diffusing light, but both have certain drawbacks. This is how the methods of treating float glass are very aggressive and "injure" the surface of the glass whose mechanical strength is reduced. In addition, the surface has lost the characteristics which are those of a "fire polish" and it becomes dirty and difficult to maintain. As for printed glasses, the performance they provide is often poor and always very different from that of diffusing glasses obtained by treatment of float glass.

The mission of the invention is to provide a diffusing glazing which has the optical quality of the treated float glass without having the disadvantages, that is to say, in particular, which is not dirty, which has good resistance to bending, and the details of the structure of which are not visible from a short distance.

Two techniques of the prior art which make it possible to obtain a flat glazing with a diffusing surface the more commonly used is the sanding of a polished flat glass on both sides such as a float glass. Sandblasting techniques are widely used in multiple industries, they are practiced in closed enclosures in which a pump produces the circulation of an abrasive powder (sand of defined particle size, corundum ...) suspended in air under pressure . This sanding makes it possible to treat surfaces by attacking them to a greater or lesser depth, the result obtained is variable, from a simple cleaning of the surface to a deep restructuring. Applied to a polished glass plate, the method makes it possible to obtain a regularly matt surface which, depending on the depth of its reliefs, diffuses more or less light both in transmission and in reflection. Sometimes for various technical and / or aesthetic reasons, it is desired to maintain good transparency on certain areas of the glass plate. To achieve the result, it suffices to protect the interesting part with an elastomer film before introducing the plate into the enclosure. The products used are for example polychloroprene in sheets or latex deposited with a brush. The affected area will appear intact after detachment of the elastomer. The purpose of such transparent zones in the middle of totally diffusing surfaces can be to allow an observer who approaches his eye of the glazing to see perfectly from the other side, without being himself observed. It is also possible by the same method, to obtain various aesthetic effects.

The sandblasting technique is very simple to implement and it allows the desired reserves to be obtained with great flexibility. The products obtained however have two serious drawbacks which greatly limit the use of the sanding technique: the sanded glazing is weakened and very dirty. One notes the greatest brittleness of sandblasted glass if one compares its resistance to bending (four point method) of basic float glass to that of an identical sandblasted sample, one notes that the value of the stress at the breaking point passes from 200 to 50 MPa. A disadvantage practical lies in the ease with which the sanded glasses get dirty. Fingerprints, in particular, leave marks on their surface that are very difficult to clean. The only way is to use strong solvents and act mechanically by brushing vigorously.

The other method used to make a float glass diffusing, chemical attack, overcomes the two previous drawbacks. Acid matting techniques are well known to specialists. More or less viscous solutions, pastes, are marketed. They are all based on hydrofluoric acid to which are added various chemicals such as for example ammonium fluoride and fillers. The difficulty of this technique lies in its implementation: the products in question are very active and it is very difficult to make them act regularly. Screen printing techniques can be used for this through a polyamide textile sieve placed on the glass surface while the paste is moved on the upper face of the sieve using a squeegee. Another technique, that of French patent FR-A-1 503 587, proposes using the aggressive solution in the form of an aerosol so as to obtain the condensation of calibrated droplets on the glass. The product obtained is regular and does not have the disadvantages of the sanded product in particular, if the implementation of the method is careful, the mechanical resistance of the product is of the same order - and even sometimes better than that of the base glass. On the other hand, the surface condition obtained is such that the fingers generally leave no trace there.

However, the acid matting technique shows two types of drawbacks, on the one hand it poses problems relating to the environment and on the other hand it does not allow easy obtaining of mixed glazing, diffusing for certain parts of its surface, transparent for the rest. Regarding this last point, the protections that could be placed on the surface of a float glass to prevent the mating of the area concerned have annoying extra thicknesses for screen printing and secondly, the chemical solutions are so aggressive that they penetrate under the protections and prevent obtaining clear delimitations at the border of the two zones. The dangers of the industrial use of hydrofluoric acid are well known, as much for the men as for the environment without it being necessary to dwell on it.

Methods for leaving a given imprint on the hot glass have also been used in order to obtain special optical effects on the finished product.

Patent US-A-1,718,824 thus proposes, using a table casting technique, to print in the surface of the glass a diffusing background thanks to a structure comprising holes which make the glazing translucent with a "frosted" surface. This diffusing background is interrupted by grooves with a V section which refract the light. This structure of the glass surface is the imprint left by that of the table on which the glass is spread before being rolled by a roller which leaves it, an unstructured surface on the other side.

A more recent technique which relates to glass or plastic plates and which evokes the rolling of glass between two rollers is described in patent FR-A-1 281 723. Its principle is to obtain a moire effect by printing on each of the faces of the glass a regular pattern consisting of regular rows of small conical prisms or circular cones in relief and / or in hollow, the originality of the technique consisting in depositing the rows of a face so that they make a low angle with the rows of the other.

The techniques described in the two previous patents, either do not give any details on the diffusing structure like the first which speaks of "the usual way" of producing the "frosted" surface or else like the second show a very coarse structure where the no cones of revolution is of the order of the thickness of the glass plate. What is essential for produce the announced geometric figures.

The solution proposed by the invention for obtaining diffusing flat glasses makes it possible to avoid the drawbacks of the previous sandblasting or acid matting techniques without using the same means as those of the prior art.

The invention proposes a diffusing glazing obtained by rolling hot glass and in which the imprint imprinted in the glass in the diffusing areas consists of pyramidal craters, all identical, separated from each other by distances less than their largest dimension, these craters are preferably hexagonal, they are often truncated pyramids. The bases of the craters are in circles of diameter between 0.5 and 1.7 mm and the distance between two neighboring craters is less than a third of the diameter. The glazing of the invention has pyramidal craters whose characteristics are such that they give it a diffusing structure which is not visible to the naked eye at a distance of at least 6 meters. In a variant, the distance from the centers of two neighboring craters is less than 1 mm and the characteristics of the pyramidal craters other than the distance from their centers are such that the fraction of the transmitted transmitted light is greater than 20%. Optionally, the preceding diffusing zones enclose diffusing zones with patterns of greater pitch. In another variant, the glazing comprises, in addition to the diffusing parts, transparent areas which are hollow on the surface of the glass with a substantially flat bottom, their depth is between 0.5 and 1 mm and is preferably 0 , 8 mm.

The invention further relates to the method for obtaining a diffusing glazing by a hot rolling technique in which the glass is laminated between a smooth lower roller and an upper roller comprising identical pyramidal pints regularly spaced whose distance between them is less to the greatest dimension. They are preferably trunks of hexagonal pyramids.

The invention also relates to the roller for producing by diffusion a diffusing glass, it comprises identical pyramidal points regularly spaced and the distance separating the bases of the pyramids is less than their largest dimension, moreover, the pyramidal points are trunks of hexagonal pyramids and the bases of the pyramids are inscribed in circles of diameter between 0.5 and 1.7 mm. In a variant, the distance from the centers of two neighboring pyramidal points is less than 1 mm. Furthermore, the roller has smooth raised areas at the top substantially parallel to its surface and whose thickness is between 0.5 and 1 mm and is preferably 0.85 mm.

The techniques of the invention thus make it possible to obtain, with simple means, of a traditional implementation in industry, without danger to the environment, high-performance products which do not have the drawbacks of the prior techniques: choice of geometric pattern helps control diffusion, the surface does not get dirty and is easy to maintain. As for the transparent areas that can allow vision, they are very easily obtained and do not require any additional labor.

The figures and the description which follow will make it possible to understand the operation of the invention.

Figures 1,2,3 and 4 show the appearance of the surface of the laminated glass according to the invention immediately after rolling.

Figure 5 shows the appearance of laminated glass with its viewing areas.

Figure 6 presents the statistical results of the bending tests.

The technique of the invention is a rolling technique. The rolling of hot glass between two rollers has been a known technique since the manufacture of flat glass has become industrial. The pasty glass which flows by overflowing from the tank of an oven heated either by flames above the bath, or by Joule effect in the bath itself goes towards two horizontal rollers, of steel which carry it inside giving the shape of a plate of determined width and thickness but of indefinite length. At least one of the rollers, generally the upper roller, has a peripheral surface with a relief.

This structured surface is pressed onto the surface malleable glass during lamination and it is very soft at this temperature takes the imprint of this structure at this instant. However, since glass has a significant thermal inertia, its surface does not freeze instantly. The stresses introduced into the mass of glass during printing tend to relax, causing surface creep. All these phenomena explain why the relief of the surface of the roller is not found - in negative - on the surface of the glass after it has cooled: if we can precisely define the structure of the printing roller, the resulting structure on cold glass, the resulting imprint, cannot be defined with precision. When we want to obtain a given optical effect with a printed glass, the best way to characterize this glass is to precisely define the relief it had at the time of rolling, when the surface structure of the roller has plowed its surface. This structure is the replica, the shape exactly complementary to that of the roll.

To achieve the object of the invention, that is to say obtain an optical effect, a diffusion of light, which has the same qualities as that produced by a matte glass with sand or acid, that is to say , a regular distribution of the transmitted light, without preferential orientations and the absence of structure visible to the naked eye at a distance greater than six meters when the sample is illuminated in diffuse light, it was discovered that it was enough to 'Use an upper roller with pyramidal points separated by "flat" areas (which actually follow the surface of a cylinder of revolution at the periphery of the roller), the lower roller, meanwhile, is smooth.

In Figure 1, there is shown a first example of the relief printed in the mass of the glass during rolling. According to the invention, the roller had pyramidal points separated by "flat" areas. The spikes were pyramid trunks with a square base. The relief obtained on the hot glass has, in negative, the same relief. We see in 1, the surface remained flat. The base square of the pyramid leaves its trace in 2 and its lateral surfaces in 3 and the truncated top produces the square imprint at the bottom of the crater 4. As soon as the impression was made in the pasty glass at the time of rolling all the sharp angles fade. This is in particular the case for the edges 5 of the imprint. The pyramidal points of the roller are staggered and it is obviously the same for the craters which mark the surface of the glass. The dimensions of the pyramidal points at their base were 0.5 x 0.5 mm and at their truncated top 0.25 x 0.25 mm. The distance between two parallel sides which is the same in both directions to obtain an isotropic optical effect was 0.5 mm. The lateral face of the pyramid made an angle of approximately 45 ° with the plane of its base.

In Figure 2 the pattern shown consists of "diamond points". The pyramids, always with a square base, are not truncated. They are also staggered, the alignments form rows parallel to the sides of the bases of the pyramids and the distance from two successive axes is 1.5 times the side. The side of the squares is 0.5 mm.

In FIG. 3, the arrangement is the same as in FIG. 2, but here the shape of each pyramidal point is particular. The lower part of the point is that of a square pyramid, but, halfway up the summit, the figure is inverted and the surface descends, recessed inside the base. The imprint obtained on the hot glass is shown in the figure. We see in 6 the surface remained flat, in 7 the sides of the large pyramid, hollow in the glass. In 8 we find the square which constitutes the cusp line and finally, in 9 the tip of the inverted pyramid. As, in the example, the turning back was carried out at mid-height, the point 10 of the small pyramid was located substantially at the level of the surface remained flat of the glass 6.

The principle of the pattern in Figure 4 is the same as that in Figure 1, the difference being in the shape of the pyramidal points which are hexagonal here. The form obtained in hot glass consequently consists of hexagonal cavities with a flat bottom. The preferred shape for the pyramid is one that has an angle of 60 ° between the base and the faces. The height of the pyramid trunk is half the diameter of the circle circumscribed at the base polygon.

Two variants of the preceding pattern were produced, one, type A, with a distance 11 between rows of pyramids of 0.7 mm and another, type B, with a distance of 1.7 mm. The distance 12 between two neighboring pyramids in the same row is also 0.7 and 1.7 mm respectively. The base of the pyramid is in a circle with a diameter of 0.7 mm for type A and 1.67 mm for type B. It follows that the pyramids of type A have their bases in contact with each other the others while those of type B have the sides of their bases spaced 0.20 mm apart in the same row and 0.55 mm apart from row to row.

The diffusing effect of the glazing according to the invention is obtained by the juxtaposition of the preceding pyramidal craters. Light scattering measurements were carried out on both type A and type B samples, for comparison, the measurements were also made with a sandblasted float glass. The measurement consists in illuminating the sample under normal incidence with a parallel beam of white light and in collecting and measuring on the other side all the transmitted light, using an integrating sphere. This has two positions, one which collects the parallel beam and the other which lets it exit through an ad hoc orifice. The measurement is made without or with sample and in the latter because, with or without the direct beam.

The most interesting measurement is that of the fraction of the transmitted light which is diffused. In the three cases, with incidence on the smooth side, we found:

In addition, mixed diffusing samples were produced which included regular "large" size patterns like those of the preceding type B and, in place of the substantially smooth intermediate pads, a fine diffusing structure, like that of the type A. The optical results are intermediate between those of type A and type B above.

The embodiment just described where the entire surface is diffusing is obviously the most effective, however, to allow vision through certain areas of the glazing or for aesthetic reasons, the invention provides insert transparent areas with a substantially flat bottom and parallel to the glass plate distributed in the diffusing parts of overall surface much larger than the sum of the areas of the transparent areas. FIG. 5 shows three examples of embodiments. The pattern 13 comprises parallel transparent bands separated by diffusing zones. The transparent lines 14 have a width of 2 mm and a depth at the time of rolling of 0.8 mm, their spacing between axes is 22 mm. The intermediate diffusing zone 15 consists of the juxtaposition of hexagonal craters 0.7 mm apart. The pattern 16 is identical in all respects except for the shape of the lines which, instead of being straight, is sinusoidal with a period of 30 mm. As for the pattern 18, it includes isolated areas diffusing similar to the preceding areas clear 19 which are squares of 2 mm side placed themselves so as to produce a square mesh with a pitch of 9 mm. On the surface of the glass, the indentations of the squares 19 have a depth of 0.8 mm.

The object of the invention is to provide diffusing glazing units having properties equivalent to or better than those of glazing units obtained by sandblasting or acid matting techniques while being cheaper and non-polluting. Among the performances, the fact that the laminated glasses are insensitive to fingerprints is well known and from this point of view, the glazings of the invention have properties far superior to those of sandblasted glasses. We also wanted to obtain better mechanical performance. Bending tests were therefore carried out. These are carried out on a dynamometer marketed by INSTRON on 4 mm thick samples with a length of 80 mm and a width of 40 mm. The bending device is said to be "with four supports" and it makes it possible to obtain a uniform stress on an area of 40 X 40 mm. For each type of glass, we measured around thirty samples and we proceeded to a statistical analysis, we plotted in particular the lines of WEIBULL which show that in the five cases, the distribution was substantially Gaussian.

These lines are shown in Figure 6. The natural logarithm of the breaking stress σ in megapascals and ordinates is plotted on the abscissa, the cumulative percentage of the samples whose breakage occurred for a constraint corresponding to the abscissa concerned. The percentage scale corresponds to the Gaussian distribution. In Figure 6, we see at 20, the behavior of a sanded sample. In 21, is the line of WEIBULL of type B samples, that is to say obtained with hexagonal pyramidal points with a pitch of 1.7 mm. 22 is the WEIBULL curve of type A, that is to say with a pitch of 0.7 mm. On the other part of FIG. 6, we see with a different abscissa scale, at 23 the same straight line (corresponding to type B). In 24 we see the synthesis of the bending results obtained with a laminated glass with two smooth faces.

The median values of the four types of glass are shown in the table.

This table shows that the results obtained with the laminated glasses of the invention are intermediate between those of a smooth laminated glass and those of a sandblasted glass.

Claims (20)

1. Diffusing pane, produced by hot rolling of glass, characterized in that the imprint printed into the glass in the diffusing areas is composed of pyramidal craters, all identical and separated from one another by distances smaller than their largest dimension.
2. Pane according to Claim 1, characterized in that the pyramidal craters are chosen from among those having a hexagonal or square base.
3. Pane according to Claim 2, characterized in that the pyramidal craters are truncated pyramids.
4. Pane according to Claim 3, characterized in that the bases of the craters can be inscribed in circles having a diameter of between 0.5 and 1.7 mm.
5. Pane according to Claim 4, characterized in that the distance between two adjacent craters is less than one-third of the diameter.
6. Pane according to one of the preceding Claims, characterized in that the characteristics of the pyramidal craters are such that the diffusing structure is not visible to the naked eye at a distance of at least 6 metres.
7. Pane according to one of the preceding Claims, characterized in that the distance between the centres of two adjacent craters is less than 1 mm.
8. Pane according to Claim 7, characterized in that the characteristics of the pyramidal craters other than the distance between their centres are such that the fraction of the transmitted light diffused is greater than 20%.
9. Pane comprising diffusing areas according to one of the preceding Claims, among which are interposed diffusing zones having motifs of a larger pitch.
10. Diffusing pane according to one of the preceding Claims, characterized in that it comprises, in addition to the diffusing parts, transparent areas.
11. Pane according to Claim 10, characterized in that the transparent areas are recessed from the surface of the glass with a substantially flat base.
12. Pane according to Claim 11, characterized in that the depth of the transparent areas is from 0.5 to 1 mm and is preferably 0.8 mm.
13. Method of producing a diffusing pane by a hot rolling technique, characterized in that the glass is rolled between a smooth lower roller and an upper roller comprising uniformly spaced, identical pyramidal points, the distance that separates them being less than the largest dimension.
14. Method according to Claim 13, characterized in that the pyramidal points are truncated hexagonal pyramids.
15. Roller for producing by rolling a diffusing glass, characterized in that it comprises identical pyramidal points, uniformly spaced in such a way that the distance separating the bases of the pyramids is less than their largest dimension.
16. Roller according to Claim 15, characterized in that the pyramidal points are truncated hexagonal pyramids.
17. Roller according to Claim 16, characterized in that the bases of the pyramids can be inscribed in circles of a diameter between 0.5 and 1.7 mm.
18. Roller according to one of Claims 15 to 17, characterized in that the distance between the centres of two adjacent pyramidal points is less than 1 mm.
19. Roller according to one of Claims 15 to 18, characterized in that it comprises smooth areas in relief, having the upper part substantially parallel to its surface.
20. Roller according to Claim 19, characterized in that the thickness of the smooth areas is from 0.5 to 1 mm and is preferably 0.85 mm.

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